In Vienna, Europe's second-largest cemetery has embraced biodiversity – without disturbing the dead.

Some of the greats are here. Beethoven, Schubert, Brahms. As well as the Hollywood pin-up-turned-inventor Hedy Lamarr – oh, and Austrian rock icon Falco. This is their final resting place.

But tread carefully through the Vienna Central Cemetery in the early hours of the morning and you might catch a glimpse of something moving between the weathered headstones. Not ghosts – but puffy-cheeked European hamsters. They're very much alive.

These adorable mammals reside in the Park of Peace and Power on the northern side of the cemetery. Narrow trails on the ground reveal where they have been scurrying lately. Once considered a pest, the hamsters are now critically endangered in Europe. Urbanisation and industrial farming have decimated their habitat in recent decades, and should their population continue to decline, they are likely to be extinct by 2050 according to the IUCN Red List. For now, they're clinging on to life here – in Europe's second-biggest cemetery. As unlikely as it might seem, this place is a perfect home for them. The landscapers are careful not to disrupt their burrows, and visitors like to leave snacks for them. In winter, when their natural food supply runs low, the hamsters often pilfer candles from nearby graves to eat the oil-rich wax.

Urban cemeteries are overlooked biodiversity hubs even though they are similarly valuable to urban parks in terms of species conservation. A 2019 review of graveyard biodiversity identified 140 protected species in cemeteries around the world, from the orchids of Turkish cemeteries to the increasingly scarce steppe vegetation found on burial mounds in Eurasia.

As places of tranquillity with great cultural and spiritual importance to many, cemeteries have largely missed the effects of urbanisation that have taken place in their surrounding cities during recent centuries. As such, they represent refuges for local wildlife and can serve as stepping stone habitats – small patches of nature that animals use to migrate between larger natural areas. This is especially crucial in cities, where green spaces are shrinking and animal habitats are increasingly fragmented.

The wild inhabitants of the vast Vienna Central Cemetery, which spans 2.4 sq km (0.9 sq miles), are watched over by Thomas Filek, researcher at the University of Natural Resources and Life Sciences in Vienna. Walking across the meadow that has become home to the European hamsters, he points out their small burrows in the tall grass. "We've talked to the gardeners about working in a way that protects biodiversity, and not mowing everything is a big part of it," says Filek. "It's important to think in cycles – it starts with plants, they bring insects, the insects bring birds and so on."

Filek has been documenting local biodiversity with the help of citizen scientists here since 2021 as part of a wider project called Biodiversity in the Cemetery (Biodiversität am Friedhof), which encompasses other graveyards around Austria. The project, based at the University of Natural Resources and Life Sciences in Vienna, receives over 3,000 sighting reports from citizen scientists across different cemeteries every year.

Besides the hamsters, the Vienna Central Cemetery is also home to endangered species protected by the EU Habitats Directive including the European green toad, the Alpine longhorn beetle and the European ground squirrel. The Eurasian hoopoe, which is common in Europe but

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